Devices for determining the level of a liquid within a container are well-known in the art. Examples can be found in GB 2 126 342 or WO 2012/113776. These devices comprise a piezoelectric element which is energized so as to generate vibrations. These vibrations are transmitted into the wall of the container containing the liquid of which the level is to be determined. If the device is pressed against the wall of the container at a height which is below the level of the liquid, oscillations generated within the container by the vibrations propagate through the liquid. These oscillations are reflected at the inner wall of the container at a point opposite to where the measuring device introduced the vibrations into the wall of the container. The reflected oscillations are received by the piezoelectric element and result in a voltage which is generated within the piezoelectric element. If the device is pressed against the container at a height which is above the level of the liquid, oscillations generated in the interior of the container by the vibrations propagate through a space which is filled with gas. As the gas dampens these oscillations, hardly any reflected oscillations will reach the wall where the measuring device is placed.
The voltage which is generated within the piezoelectric element after triggering a measurement is a signal which is indicative of the nature of the space behind the wall where the device is pressed against the container, allowing to distinguish between a space filled with gas or filled with a liquid. Depending on the signal, the device can then indicate to a user whether or not liquid is present at the level at which the device was pressed against the container.
While these devices are generally capable of correctly identifying whether or not a liquid is present within the container at the height where the device is being pressed against the wall of the container, there are situations where the accuracy of the measurement is not sufficient.
The object of the invention is to improve the known devices and methods such that the accuracy of the measurement is increased.